Onblur vs Valuechange - TypeScript

As a programmer, you may have come across the onblur and valuechange events in TypeScript. Although both events are related to user input, they are used in different ways and have different purposes. Let's explore these two events in detail.

Onblur Event

The onblur event is triggered when an input element loses focus. This event is often used to validate user input or trigger some action once the user has finished entering data. For example, you might use the onblur event to check whether a user has entered a valid email address into a text box.

Here's an example of how you would use the onblur event in TypeScript:

const emailInput = document.getElementById("email") as HTMLInputElement;

emailInput.onblur = () => {
  const email = emailInput.value;
  
  if (!isValidEmail(email)) {
    // Display an error message to the user
  }
};

In this example, we attach a function to the onblur event of an input element with an ID of "email". When the user focuses on another element or clicks outside of the text box, the attached function is called. We then retrieve the value of the input element and check whether it is a valid email address using the isValidEmail function.

Valuechange Event

The valuechange event is triggered when the value of an input element changes. This event is often used to track the user's input in real time or to update some related elements on a web page as the user types. For example, you might use the valuechange event to display the number of characters remaining in a text area as a user types.

Here's an example of how you would use the valuechange event in TypeScript:

const textArea = document.getElementById("message") as HTMLTextAreaElement;
const count = document.getElementById("count");

textArea.addEventListener("valuechange", () => {
  const remaining = 100 - textArea.value.length;
  
  count.textContent = `${remaining} characters remaining`;
});

In this example, we attach an anonymous function to the valuechange event of a text area element with an ID of "message". The function is called every time the user types or deletes a character in the text area. We then calculate the number of characters remaining and update a separate element with an ID of "count" to display the remaining characters.

Conclusion

In summary, the onblur and valuechange events are two commonly used events in TypeScript that are related to user input. The onblur event is triggered when a user leaves an input element, while the valuechange event is triggered every time the value of an input element changes. Understanding the difference between these two events can help you write more efficient and effective code.